The present invention relates to external aircraft lighting systems, and in particular to such systems for use with night vision goggles.
Night vision goggles (NVGs) are used in military aircraft. By detecting ambient infra red light ("infra red light" should be understood to include near infra red light throughout this document) and interpreting this to produce a display visible to the pilot, NVGs considerably enhance a pilot's ability to "see" in the dark. One of the many advantages thus made possible is that external aircraft lighting in the visible spectrum becomes (in certain contexts) unnecessary, and military aircraft can thus be operated in a covert mode in which no such external lighting is provided, making the aircraft harder to detect. By providing low intensity external infra red lighting, it can be ensured that aircraft remain visible to each other, e.g for collision avoidance, formation flying, location and orientation, while still providing no illumination visible to the naked eye.
Several problems arise in providing the type of external aircraft lighting needed to best utilize night vision systems.
Perhaps the most significant of these problems arises during training. Regulations imposed, for example, by the Civil and Federal Aviation Authorities require aircraft in Civil airspace to carry visible external lighting. Thus, even during training in the use of night vision goggles, this visible lighting must be provided. Unfortunately, conventional lights (using filament bulbs) emit strongly in the IR part of the spectrum and thus can dazzle and effectively incapacitate NVGs, making training difficult or impossible.
In addition, many existing aircraft are not equipped with external infra red lighting, and a retrofit lighting system is therefore needed. Difficulty arises because wiring of the lighting must extend from the cockpit to extremities of the aircraft including wingtips and tail. The cost of adding fresh sets of wiring to provide for signals to two sets of lights (visible and IR) instead of the conventional single set of visible lights is considerable, since it requires disassembly of numerous parts of the aircraft to provide access to the routes taken by the wiring.
Solutions to both of the above described problems are objects of the present invention.